(a) Field of the Invention
The present invention relates to a thin film transistor array panel and a manufacturing method thereof.
(b) Description of the Related Art
A liquid crystal display (LCD) is one of the most widely used flat panel displays since it is lightweight and occupies less space than conventional cathode ray tube (CRT) displays. An LCD generally includes a liquid crystal (LC) layer that is interposed between a pair of panels including field-generating electrodes such as pixel electrodes and a common electrode. The LC layer is subjected to an electric field generated by the field-generating electrodes and variations in the field strength change the molecular orientation of the LC layer. For example, upon application of an electric field, the molecules of the LC layer change their orientation to change polarization of incident light. Appropriately arranged polarizers partially or fully block the light, creating gray or dark areas that can represent desired images.
One panel for the LCD generally includes a plurality of pixel electrodes, a plurality of thin film transistors (TFTs) for controlling signals to be applied to the pixel electrodes, a plurality of gate lines transmitting control signals for controlling the TFTs, and a plurality of data lines transmitting data voltages to be supplied to the pixel electrodes. The TFTs include gate electrodes connected to the gate lines, source electrodes connected to the data lines, and drain electrodes connected to the pixel electrodes. The other panel generally includes a common electrode disposed on an entire surface thereof.
The TFT array panel including the TFTs includes several conductive films and insulting films. The gate lines, the data lines, and the pixel electrodes are formed of different films and they are separated by insulating films and sequentially arranged from bottom to top. The gate electrodes of the TFTs are branches or portions of the gate lines, the source electrodes are branches or portions of the data lines, and the drain electrodes are usually made of the same films as the data lines.
The gate lines and the data lines are preferably made of low resistivity material such as aluminum (Al) containing metal (e.g. Al or Al alloy) in order to minimize signal delay or voltage drop. However, Al containing metal cannot form a contact with semiconductor doped with impurity and thus Al containing metal is usually used in the data lines and the drain electrodes along with another metal having good contact characteristics with semiconductor and materials such as transparent conductive materials.
In a bottom gate thin film transistor, good contact material is usually disposed under Al containing metal since the data lines and the drain electrodes are disposed on the semiconductor. However, since Al containing metal has poor contact characteristics with transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO) such that the contact resistance thereof is large and Al containing metal are corroded at the contacts. Therefore, the surface of Al containing metal of the drain electrodes must be etched to expose the good contact material for contact with the pixel electrodes usually made of ITO or IZO.
Since the multi-layered structure of the data lines and the drain electrodes is usually patterned by a lithography step, the data lines and the drain electrodes may be often disconnected. In addition, the removal of Al containing metal at the contacts may generate undercut that causes the disconnection of the pixel electrodes at the contacts.